img too wide in android

Hi,
I need some help on this one. It's killing me.
I'm trying to display an image in my app. I'm using xtype : 'image' in a vbox. it works fine in Chrome, even when I resize the window, the image resize. no worries.

Then I build in native for android. On the phone, galaxy S3 level 16, the picture is too wide in portrait mode. the picture fill the height, cutting off the side. when I rotate in landscape, it's ok.